1. Field of the Invention
The present invention relates to a mobile network, and a data communication method therefor, wherein a home agent is connected to a home network for mobile nodes, foreign agents are connected to destination networks for the mobile nodes, each of the foreign agents directly or indirectly accommodates one or more wireless base stations, and data to be transferred from the home agent to the mobile nodes is transferred to the mobile nodes through the destination foreign agents and the wireless base stations in the destination networks.
2. Description of the Related Art
In the non-patent document 1, a mobile Internet Protocol (IP) has been standardized as a technology by which an Internet node can continue communication with the same IP address even if the node moves between different networks. In the mobile IP protocol, it is required to register the position of a mobile node (MN) in a destination foreign agent (FA), and a home agent (HA) in a home network every time the MN moves between different networks. Accordingly, there is caused a problem that data transfer to the MN is interrupted until the above registration is completed.
The non-patent document 2 has disclosed the following two techniques to solve the above problem: (a) a handoff technique in which the position of an MN is registered in the destination FA through the origin FA before the MN moves to a new network; and (b) another handoff technique in which data which has reached an origin FA is directly transferred to the destination FA, and, then, is delivered to an MN before the registration of the MN position is completed in the destination FA.
FIG. 5 is a schematic view showing the handoff technique described in the above (a), wherein the MN receives an agent advertisement of the destination FA (FA1), and registers the position of the MN (expressed as “Pre-Registration” in the non-patent document 2) in the destination FA through the origin FA (FA0) before the MN moves to the new network.
FIG. 6 is a schematic view showing the handoff technique described in the above (b), wherein, assuming that the origin FA0 or the destination FA1 can use through some means information (L2 trigger) on the movement of a layer 2, a two-way tunnel is established between the FAs after moving, and packets to the MN are transferred from the origin FA0 to the destination FA1 (expressed as “Post-Registration” in the non-patent document 2).
Moreover, the non-patent documents 3 and 4 has disclosed a technology, which is called “micro mobility”, and by which movement in a certain region such as cities is efficiently controlled, as a technique to reduce delays in processing and transfer for registration of the position of an MN in an HA whenever the MN moves between networks. In the non-patent document 4, it has been proposed as shown in FIG. 7 that FAs are hierarchised in a certain area, and the position of an MN is locally registered such that the position of the MN is registered only in way FAs (a GFA and RFAs in the drawing) when the MN moves in the area.
[Non-Patent Document 1] C. Perkins, “IP Mobility Support for IPv4”, RFC3344, IETF, 2002.
[Non-Patent Document 2] K. E I Malki, “Low Latency Handoffs in Mobile IPv4”, draft-ietf-mobileip-lowlatency-handoffs-v4-07, IETF, 2003.
[Non-Patent Document 3] C. Willims, “Localized Mobility Management Goals”, draft-ietf-mipshop-lmm-requirements-02, IETF, 2003.
[Non-Patent Document 4] E. Gustafsson, et al. “Mobile IPv4 Regional Registration”, draft-ietf-mobileip-reg-tunnel-08, IETF, 2003.
In conventional technologies, there is required an assumption that it should be known, before the MN moves, which of FAs is a destination FA, or it should be understood, after the MN moves, which of FAs is an origin FA, because the origin FA and the destination FA relay and transfer data to the MN before mobile IP registration of the position. Accordingly, there are the following problems when a communication method such as a wirelesses LAN as represented by IEEE 802.11 is used:
(1) When the origin FA requires the destination FA to register the position of an MN before the MN moves,
in the first place, it is difficult for an FA on a communication network to acquire information on a subsequent destination of the MN beforehand, because the MN takes the initiative in moving, and
in the second place, it is difficult for an FA on a communication network to securely acquire the IP address and the MAC address of the destination FA beforehand, because movement of the layer 2 is started, based on the status of the wireless channel for the MN; and
(2) when a destination FA requires an origin FA to transfer data to an MN after the MN moves,
in the first place, after the MN moves, and before mobile IP registration request of the position, it is difficult for the destination FA to find the origin FA,
in the second place, it is difficult for the destination FA to know the HA of the MN beforehand before mobile IP registration of the position, though the HA for the MN has information on the origin FA, and
in the third place, though it can be thought that the MN has information on the origin FA, and the information is transmitted to the destination FA, the MN is required to recognize, in order for the MN to recognize the destination FA, by using a mobile IP mechanism for movement detection that the MN itself moves, and it takes a time to realize the above described process.
When a communication method such as the wireless LAN is used, the above described problems have made it difficult to apply a conventional handoff technique without alteration to the method.